September 1, 2010

Multiple sclerosis (MS) is a debilitating autoimmune disease, although some new studies have raised the possibility that there is more than one pathway to the final pathological changes, and that different pathways may predominate in different clinical forms of MS. It has two major components, ie, axonal degeneration and inflammation, resulting in loss of the myelin-coated axons in the central nervous system (CNS). MS is most commonly seen in the adult Caucasian population of Western European ethnic origin, and most frequently affects women aged 20–40 years.4 A definite diagnosis of MS requires the occurrence of at least two neurological events consistent with demyelination that are separated both anatomically in the CNS and temporally. There are three clinical forms of the disease, the most common being the relapsing–remitting form (RRMS), which is characterized by episodes of neurological impairment followed by complete or nearly complete recovery.

Prevalence: Globally, the median estimated prevalence of MS is 30 per 100,000, with a range of 5–80. Regionally, the median estimated prevalence of MS is highest in Europe at 80 per 100,000, followed by the Eastern Mediterranean (14.9 per 100,000), and the US (8.3 per 100,000). The countries reporting the highest estimated prevalence of MS are Hungary (176 per 100,000), Slovenia (150), Germany (149), and the US (135). The total estimated female:male ratio is around 2.0, and the prevalence rates reported are higher for women. Other studies in the US have reported a prevalence of 58–95 per 100,000. Moreover, in the past 25 years, prevalence studies of specific US regions have produced a range of estimates, up to 177 per 100,000 in Olmstead County, Minnesota.

Incidence: Globally, the median incidence of MS is 2.5 per 100,000. Regionally, the median estimated incidence of MS is greatest in Europe (3.8 per 100,000), followed by the Eastern Mediterranean (2), and the US (1.5). The countries reporting the highest estimated incidence of MS include Croatia (29), Iceland (10), and Hungary (9.8).

An interesting paper published by Patricio Abad and collegues showed that the prevalence of MS in Ecuador goes from 0.75 to 5.05 per 100,000 inhabitants being most frequent in Quito. The paper is:

Introduction: Multiple sclerosis (MS) is less frequent in areas near to the Equator, while the incidence and prevalence rises with increasing distance from this particular area, determining a clear north to south gradient. During the last decade several published reports provide recent data on the prevalence in Latin America. The main objective of this article is to report prevalence data in the three largest cities of Ecuador, a South American Country located on Latitude zero North-South.

Methods: In order to determine the prevalence and other epidemiological variables we conducted a cross-sectional, observational study in the three largest cities of Ecuador. Based on capture and recapture methodology we identified patients with MS who received medical care in the 12 state and private hospitals and in the Ecuadorian Foundation of Multiple Sclerosis (FUNDEM-Quito). The main inclusion criteria to determine the diagnosis of MS was based on the criteria proposed by Poser. For the relative and absolute frequencies calculation, as well as the 95% confidence interval, the EpiInfo 6.01 and EpiDat 3.1. programs were used.

Results: A total of 159 patients were identified in the three largest cities included in the study. In Quito, the capital city: 5.05/100,000 inhabitants (95% CI, 4.03-6.03), Guayaquil, on the coast: 2.26/100,000 inhabitants (95% CI, 1.62-2.91) and Cuenca in the south: 0.75/100,000 inhabitants (95% CI, 0.024-0.175).

Conclusions: Ecuador is a low prevalence country although we believe it is possible that the number of MS cases is underestimated since this is not a population based study. We believe that more studies should be carried out on general populations where the disease has been seldom reported or as non-existent. Important exogenous factors may be involved in the pathogenesis of MS in Ecuador.